1. Field of the Invention
The present invention relates to a control device, and more particularly to a control device for maintaining a chemical mechanical polishing machine in a wet mode.
2. Description of the Prior Art
In semiconductor processing, protuberances of the deposited layer on the semiconductor wafer must be removed and unevenness of the semiconductor wafer must be eliminated through the execution of a planarization process. At the present time, chemical mechanical polishing (CMP) is the most widely performed global planarization method used in which a semiconductor wafer undergoes mechanical contact polishing on a CMP machine by sprinkling a chemical reagent onto the wafer and causing a particular chemical reaction. This increases the polishing rate.
Please refer to FIG. 1 and FIG. 2. FIG. 1 is a top view of the chemical mechanical polishing machine 10 according to the prior art. FIG. 2 is a sectional schematic diagram along line 2--2 of the chemical mechanical polishing machine 10 shown in FIG. 1. The CMP machine 10 comprises a polishing table 12, a polishing pad 14 positioned on the polishing table 12, a slurry sprinkler 16 for sprinkling liquid onto the polishing pad 14, and at least one carrier head 18. The carrier head 18 supports a semiconductor wafer 20 as it brings the semiconductor wafer 20 in contact with the polishing pad 14 where the CMP process takes place.
The liquid sprinkled from the slurry sprinkler 16 is a chemical agent formed from a mixture of colloidal silica or dispersive alumina with alkaline potassium hydroxide (KOH) or ammonia (NH.sub.4 OH) solution. The liquid comprises large quantities of hard polishing particles with a particle size distribution around 0.1 to 2.0 um. The chemical characteristics of this liquid and the highly abrasive particles are employed during the CMP process. Further adjustment of process parameters such as the temperature of the slurry, the rate of feeding or the polishing rate and matching of the material of the polish pad 14 is accomplished, the CMP process can be then performed to even out the semiconductor wafer 20 through chemical removal.
However, if the CMP machine 10 is not continuously maintained in a wet mode after the CMP process is completed, the residual liquid may dry on the polishing pad 14 and the carrier head 18 or even solidify within the pipeline of the slurry sprinkler 16. This would result in clogging of the pipeline. Later, when performing the CMP process again, this solidified liquid debris might be released from the slurry sprinkler and become distributed onto the CMP machine 10 to cause scraping of the surface of the semiconductor wafer 20. Also, the semiconductor wafer 20 may get caught on the carrier head 18 and become damaged or even crack as a result.